This application is a 371 of PCT/JP99/03900 filed Sep. 9, 1999.
The present invention relates to a member with a film formed by a thermal spray material for applying special properties which is thermally sprayed onto products, equipments, members, and the like which are manufactured or employed in various fields, such as steel making, ship building, paper making, automobile manufacture, household appliance manufacture, office equipment manufacture, construction, and the like, which require molten metal corrosion resistance, molten salt corrosion resistance, resistance to oxidation, resistance to thermal shock, resistance to build-up, chemical resistance, salt water resistance, and the like.
Conventionally, ceramic was thermally sprayed onto a portion of structural members in the various fields described above; however, it cannot be said that the members employed had thermal spraying over the entire surface thereof.
The reason for this was that, although ceramic is superior in the desired corrosion resistance, resistance to high temperature oxidation, and resistance to build-up with metals and the like, it is not clearly superior to cermet, and furthermore, there are problems with the strength, minuteness, adhesion, and resistance to thermal shock of the coating, so that it was difficult to actually apply.
Representative conventional ceramic thermal spray materials included, for example, Al2O3, Cr2O3, MgAl2O4, Al2O3+TiO2, and the like.
In the conventional materials described above, the conventional materials described above were unsatisfactory in that they either did not exhibit sufficient properties, or had desirable properties but also had defects. For example, Al2O3 and Cr2O3, which are known as the most common ceramics, had the following problems.
Al2O3: this substance itself has good oxidation resistance and resistance to chemicals; however, a large number of cracks is formed in the coating film which is formed, and gas and solutions and the like penetrate along these cracks and erode the material, so that peeling of coating film is caused. As a result, there is no oxidation resistance or resistance to chemicals.
Cr2O3: the problem is the same as Al2O3; in particular, in molten zinc baths and the like containing Al, as the concentration of Al increases, Cr2O3 is reduced by Al, so that the layer itself is eroded.
Furthermore, as a defect which is essentially common to these, the thermal spraying efficiency is low.
In order to eliminate these deficiencies, in Japanese Patent Application No. HEI 9-122904, the combination of various oxides containing rare earths is disclosed. Additionally, in Japanese Patent Application, first publication No. HEI 4-350154, the addition of SiO2 to other oxides and an improvement in the resistance to thermal shock is disclosed. However, these proposals only involve the simple combination of various oxides, so that while the advantages of one oxide are present, the disadvantages of another oxide are simultaneously present, so that, although there is some effect, it was unsatisfactory.
The present invention solves the problems present in the prior art described above, and has as an object thereof to provide a thermal spray material capable of forming a coating film satisfying all characteristics, and members having a coating film formed using this thermal spray material.
As a result of diligent investigations with the object of attaining the object described above, the present inventors have discovered that a coating film having as a chief component thereof a double oxide of rare earths or a double oxide containing rare earths is superior in all required characteristics and have thus arrived at the present invention.
The present invention, which is based on the discovery described above, has as an essential point thereof, a thermal spray material which contains one or more double oxides comprising (a) one or more of the trivalent metal elements Al, Ti, V, Cr, Co, Rh, and rare earth (Sc, Y, and lanthanoid), and (b) one or more rare earth (Sc, Y, and lanthanoid) differing from those in (a).
Furthermore, a thermal spray material in which the amount of the double oxide described above contained is 5% by volume or more, the remainder comprising one or more metal oxides, excluding the Group Ia metals, or oxides of Si, is also an essential point of this present invention.
Furthermore, a member having a coating film formed by the thermal spray material described above is also an essential point of the present invention.
The structure and function of the present invention will now be explained.
The double oxide of the thermal spray material structural component of the present invention is a monophasic oxide comprising a plurality of object structural metals, and is a phase differing from all the oxides of the simple substances of the structural metal elements. In many cases, the double oxide employed in the present invention is one which has a crystalline structure differing from the oxide from each structural metal simple substance (crystalline structures such as ilmenite structures, perovskite structures, and garnet structures and the like); however, there are many for which the structure is not known (particularly in the case of multi-element systems), and there are many which are not listed in JCPDS (Joint Committee on Powder Diffraction Standards: published by International Center for Diffraction Data).
The thermal spray material of the present invention contains the double oxides as defined above. With respect to this point, the concept is different from the simple combination of oxides in the invention of Japanese Patent Application No HEI 9-122904 discussed above.
Oxides, hydroxides, carbonates, and chlorides of organic acids may be employed as the double oxide structural raw material of the thermal spray material structural component of the present invention. The following manufacturing methods may be adopted:
a. A method in which the predetermined raw materials are mixed, and are melted in an arc furnace or the like, and are then pulverized and classified.
b. A method in which the raw materials are first mixed, then molded, sintered, pulverized, and classified.
c. A method in which the raw materials are mixed, and then the mixture is granularized, sintered, pulverized, and classified.
d. A method in which microgranules of the double oxide produced by the sol-gel method are granularized, sintered, pulverized and classified.
e. A method in which one or two or more types of double oxides produced by the methods of a-d above are granularized (and furthermore, where necessary, these may be sintered, pulverized, and classified). However, the material of the present invention is not limited to these manufacturing methods.
The grain size of the double oxide after pulverization and classification may be determined by the thermal sprayer which is employed; however, this is roughly within a range of 500-5 micrometers.
Furthermore, in the present invention, the double oxides described above can be used by themselves as thermal spray materials; however, as a result of the adjustment of the thermal expansion with the substrate, or for economic reasons, depending on the use, it is preferable to thermally spray a thermal spray material containing these double oxides in an amount of at least 5% by volume, the remainder comprising one or more of metal oxides excluding the Group Ia metals or oxides of Si. When the double oxide is contained in an amount of less than 5% by volume, the effects thereof can not be expected. It is also possible to mix these oxides; however, a complex, in which one oxide is distributed within another oxide, is more preferable.
Furthermore, depending on the use, in order to reduce residual stress within the coating film, a bond coat of a hot corrosion resistant alloy such Nixe2x80x94Cr, Coxe2x80x94Cr, Coxe2x80x94Crxe2x80x94Mo, MCrxe2x80x94Alxe2x80x94Y, or the like, or a cermet material having a certain degree of corrosion resistance to molten metals comprising WCxe2x80x94Co, WBxe2x80x94WCxe2x80x94Co, or like, may be employed, and this does not limit the present invention.
The thickness of the coating film is preferably within a range of 5-1000 micrometers depending on the use; however, a range of 10-500 micrometers is preferable for the development of the residual stress effect.
Furthermore, a sealing treatment may be executed by impregnating or firing, onto the coating film, a solution having as the chief component thereof one of dichromic acid (H2CrO4 and/or H2Cr2O7), and inorganic colloidal compound, or a metal alkoxide or the like, and these applications do not limit present invention.